A polyurethane is produced by reacting a polyester polyol or polyether polyol, and a polyisocyanate in the presence of a chain lengthening agent such as a low-molecular weight diol, diamine or the like, if necessary. A polyurethane which is produced by using a polyester polyol is inferior in resistance to hydrolysis in composition with a polyurethane which is produced by using a polyester polyol. On the other hand, the use of polyurethanes which are produced by using polyether polyols is limited due to the problematic nature of their dynamic physical properties, weatherability, oil resistance, and solvent resistance.
Although polyurethanes which are produced by using polycarbonate polyols improve on the above described disadvantages, their cold resistance is inadequate, and they are extremely expensive, thus limiting their industrial use.
Heretofore, as a polyester polyurethane with a comparatively excellent resistance to hydrolysis, a polyurethane which is produced by using a polycaprolactone polyol is known [Polyurethane Resine Handbook, published by Nikkan Kogyo Shinbunsya (Sep. 25, 1987)].
In addition, examples of polyester polyurethanes derived from a chain diol possessing an alkyl side chain are known, i.e., neopentylglycol-derived or 2-butyl-2-ethyl-1,3-propanediol-derived polyester polyurethanes (Japanese Published Unexamined Patent Application No. 229918/85) and 3-butyl-1,5-pentanediol-derived polyester polyurethanes (Japanese Published Examined Patent Application No. 54966/92); however, from the standpoint of water resistance and the like, these compounds are inadequate for practical use.
There are descriptions of a polyester polyurethane formed from a chain diol possessing an alkyl side chain in Japanese Published Unexamined Patent Application No. 81414/92 and Japanese Published Unexamined Patent Application No. 262859/93, however there exists no concrete disclosure regarding a polyurethane which is produced by using a polyester copolymer derived from 2,4-dialkyl-1,5-pentanediol and 2,2-dialkyl-1,3-propanediol.
On the other hand, W096/09334 discloses a polyester polyurethane derived from 2,4-diethyl-1,5-pentanediol as a polyurethane exhibiting excellent resistance to hydrolysis, weatherability, and alkali resistance. The polyurethane derived from 2,4-diethyl-1,5-pentanediol alone as the diol component of the starting material for the polyester polyol described in the Examples of the aforementioned application exhibits sufficient performance properties for most uses; however, under harsh usage conditions such as in the coating of underwater cables for use in petroleum exploration, connection cords of electrically powered heavy machinery or the like, the intrinsic properties of the aforementioned are insufficient from the standpoint of mechanical strength and resistance to abrasion. In addition, said application describes that 2-ethyl-2-butyl-1,3-propanediol may be added to 2,4-diethyl-1,5-pentanediol as a starting material for the polyester polyol, however no concrete description of these details exists.